Analysis of PR detector data from the GEn-RP experiment

The GEn-RP experiment E12-17-004 is among various form factor experiments with the Super-Bigbite Spectrometer (SBS) setup at Hall-A, Jefferson Lab and aims to measure the ratio of electric to magnetic elastic form factors of the neutron GEn/GMn using recoil polarimetry techniques at <span style="font-size:10.8333px">Q2 =4.3(GEv/C) in quasi-elastic electron-neutron scattering from a deuterium target. The ratio of these form factors is determined from the ratio of the transverse Px and the longitudinal Pz components of the spin polarization, that is transferred to the recoiling neutron from the incident, longitudinally polarized electron beam. Both high-momentum, small-angle neutrons produced during np-np elastic scattering and high-momentum small-angle protons produced by np-pn (charge exchange) are used to analyze the neutron polarization components after precessing through known magnetic fields. In addition, low momentum, large-angle protons produced during np-np elastic scattering in an active analyzer are detected, as a proof-of-principle measurement of the analyzing power. Large-angle protons are detected in a side arm setup of one pair of the GEMs and a hodoscope. The Active Analyzer is located between the inline GEMs and the Hadron Calorimeter to detect the forward neutron.

This experiment will yield GEn/GMn at a momentum transfer nearly three times that of the highest published Q2 point with recoil polarization. If the charge exchange analyzing power is comparably higher than that of np-np, then future recoil polarization at higher Q2 becomes feasible. Ongoing work focuses on the analysis of large-angle recoil protons to extract the analyzing power. As part of this analysis, we have studied the hit correlation between both PR GEMs and the hit correlation between GEMs and the PR hodoscope to understand the detector response and improve event selection.